A clutch mechanism has been generally used for the purpose of establishing and interrupting a transmission path of a driving force, which is generated by an engine of a vehicle, from the engine to a vehicle drive wheel. A transmission is commonly used together with the clutch mechanism, the transmission in which an input shaft an output shaft and plural gear train are provided. The input shaft is connected to the clutch mechanism. The output shaft is connected to the vehicle drive wheel. The plural gear trains respectively have different speed change ratios that are effective for the purpose of switching a rotational speed ratio between the input shaft and the output shaft. In a transmission apparatus, which incorporates, therein, the clutch mechanism and the transmission, one of the plural gear trains (a first gear train) is selected and gear-meshed, and the clutch mechanism is engaged, wherein the driving force of the engine can be transmitted to the vehicle drive wheel, and the vehicle can drive at a shift stage established by use of the first gear train. Upon a shift operation, the engagement of the clutch mechanism is once released, and another one of the plural gear trains (a second gear train), which is one step higher than the first gear train, is selected and gear-meshed. The clutch mechanism is then once again engaged.
In order to have an occupant seated on a vehicle seat obtain a pleasant feeling, recent requirements have led to improvement in a smoothness of a shift operation. For example, JP2003-120764A discloses a twin-clutch type transmission apparatus having two clutch mechanisms. A twin-clutch transmission apparatus, which is generally used, incorporates, therein, a first clutch capable of connecting a first input shaft of a transmission to an engine, and a second clutch capable of connecting a second input shaft of the transmission to the engine. On the first and second input shafts, plural gear trains are respectively mounted thereon, which respectively possess a different gear ratio. When a shift stage is selected, one of the plural gear trains is gear-meshed with a driven gear mounted on an output shaft, wherein a driving force of the engine is transmitted to a vehicle drive wheel via this twin-clutch type transmission apparatus.
Upon a shift operation while a vehicle is driving, e.g., when a gear engagement condition in a transmission is switched from a first condition, in which one (e.g. a first gear train) of the plural gear trains mounted on the first input shaft has been gear-meshed, and the first clutch has been engaged, to a second condition, in which one (higher than the first gear train) of the plural gear trains mounted on the second input shaft is gear-meshed, this shift operation can be implemented by transmitting an engine driving force by temporal use of both two clutches. More specifically, at a time that the first clutch has been fully engaged and the second clutch has been disengaged, a frictional engagement ratio between the first clutch and the second clutch is controlled. That is, a force for engaging the second clutch is gradually increased, while a force for engaging the first clutch is gradually decreased. As described above, a transmission path of the engine driving force from the engine to the vehicle drive wheel is gradually switched from a transmission path via the first clutch to a transmission path via the second clutch. That is, at the last stage of this shift operation, a driving force of the engine is transmitted to the vehicle drive wheel only by use of the second clutch. Therefore, in this twin-clutch type transmission apparatus, a smooth shift operation can be attained without interrupting transmission of the driving force.
Meanwhile, the aforementioned shift operation is performed while a vehicle is driving at an approximately constant driving speed. A rotational speed of the second input shaft (a higher side) is hence smaller than a rotational speed of the first input shaft (a lower side). Therefore, upon a shift operation, it is necessary to control an engine rotational speed to a lower value. An engine rotational speed can be controlled to a lower value by electronically restraining an amount of fuel to be supplied to the engine. In such circumstances, the second clutch has been rotated in a slip manner so that the second clutch serves as a brake for decreasing an engine rotational speed. When the shift operation is completed, the second clutch is fully engaged, and the second input shaft is rotated in sync with the engine. In this case, it is possible to again increase an engine rotational speed in response to an operation of an accelerating member.
According to the above-described technology, a clutch engagement/disengagement operation and an engine control can be implemented smoothly in such a manner that an occupant to be seated can obtain a comfortable feeling. However, this on occasions causes a long-lasting shift operation. Moreover, when a load applied to an engine is reduced in response to a slip of the first clutch, an engine rotational speed, which is actually expected to drop, is temporality increased. Therefore, fuel racing occur, wherein an amount of fuel injected at an engine and a period of time for a shift operation is increased
The present invention has been made in view of the above circumstances, and provides a transmission apparatus having a clutch, the transmission apparatus which is capable of rapidly dropping a rotational speed of an engine at a time of a shift operation and is capable of completing a shift operation in a short period of time, wherein an engine fuel racing can be prevented.